The terms "ultrasonic radiation" and "ultrasound" are employed interchangeably in this specification to designate pressure-rarefaction waves differing from sound waves in exhibiting higher frequencies and shorter wavelengths. The term "ultrasonic exposure" is employed to designate exposure to ultrasonic radiation. The production of visible images by means of ultrasonic radiation is referred to in the art as "ultrasonoscopy". The production by means of ultrasonic radiation of a record which is in, or can be converted to, a viewable form is referred to as "ultrasonography". The instruments for producing ultrasonoscopic images are designated "ultrasonoscopes", and the ultrasonoscopes which produce ultrasonographic images are referred to as "sonographic cameras". Elements which form records of ultrasonic radiation patterns as a result of being ultrasonically exposed in a sonographic camera are referred to as "ultrasonographic elements". Instruments which are capable of permitting ultrasonographic elements to be concurrently exposed in different areas to different intensities of ultrasound are referred to as "sonographic sensitometers".
The definition of terms as here presented is believed to be generally consistent with the use of these terms in the art. Specifically, most of these terms are suggested by P. J. Ernst in the Journal of the Accoustical Society of America, Vol. 22, No. 1, in an article entitled "Ultrasonography", pp. 80-83, January 1951.
In Belgian Pat. No. 864,089, dated Aug. 17, 1978 (generally corresponding to U.S. Pat. No. 4,223,082), there is disclosed a process for imagewise ultrasonically exposing an ultrasonographic element while in contact with a transport liquid to produce an ultrasonographic record which can be converted to a viewable ultrasonographic image. Specifically, it is disclosed to employ as an ultrasonographic element a silver halide photographic element comprised of a photographic support and a silver halide emulsion layer. The silver halide emulsion layer, which functions as an ultrasound recording layer unit, is placed into contact with a transport liquid, such as a polar solvent, preferably water or an aqueous solution. Following contact, diffusion between the emulsion layer and the transport liquid begins, tending to bring the emulsion layer and the transport liquid more closely into equilibrium. By imagewise ultrasonically exposing the emulsion layer, the rate of diffusion is accelerated in imagewise exposed areas. Since diffusion between the emulsion layer and the transport liquid has the effect of altering the electromagnetic radiation response of the emulsion layer, diffusion has the effect of producing in the emulsion layer a record of the image pattern of ultrasonic exposure (that is, an ultrasonographic record) which can be converted to a viewable ultrasonographic image by exposure to electromagnetic radiation, typically light, and subsequent photographic processing.
Although Belgian Pat. No. 864,089, cited above, employs silver halide photographic elements, ultrasonographic imaging processes are known which employ differing ultrasonographic elements as well as differing transport liquids in producing an ultrasonographic record.
In commonly assigned, copending patent application titled ULTRASOUND IMAGING OF INTERNALLY FOGGED SILVER HALIDE ELEMENTS, Ser. No. 3,571, filed Jan. 15, 1979, now U.S. Pat. No. 4,228,230 there are disclosed internally fogged silver halide emulsion layer containing elements useful as ultrasonographic elements. The process of ultrasonographic exposure differs from that of Belgian Pat. No. 864,089 in that no light exposure step is employed during or after ultrasound exposure in order to produce a viewable ultrasonographic image. A solute capable of revealing the internal fog in the emulsion layer is contained in the transport liquid.
In commonly assigned, copending patent application titled ULTRASONIC IMAGING WITH CATALYTIC ELEMENTS, Ser. No. 8,910, filed Feb. 2, 1979, now U.S. Pat. No. 4,225,658 ultrasonographic elements are disclosed containing a catalyst layer. Ultrasonic exposure can be undertaken while the ultrasonographic element is in contact with a transport liquid containing a catalyst poison. Light exposure is not requiring for imaging.
In commonly assigned, copending patent application titled ULTRASONOGRAPHIC ELEMENTS CONTAINING MULTIPLE LAYERS AND PROCESS FOR THEIR USE, Ser. No. 30,665, filed Apr. 16, 1979, now U.S. Pat. No. 4,269,914 there are disclosed ultrasonographic elements which contain in addition to a silver halide emulsion layer in the recording layer unit an additional layer, separated by a barrier layer, which can supplement the transport liquid in supplying or receiving diffusible ions in accelerating equilibration.
Although the above-cited disclosures differ in their specifics, each is directed to a process of recording an ultrasonic exposure pattern employing an ultrasonographic element comprised of a support and a recording layer unit. The recording layer unit is contacted with a transport liquid and imagewise ultrasonically exposed to accelerate imagewise diffusion between the recording layer unit and the transport liquid, thereby producing in the recording layer an ultrasonographic record. The ultrasonographic record can itself be viewable or can be converted to a viewable form by subsequent processing.
Ultrasonographic recording by the general process described above is limited by the maximum rate of diffusion which can be induced by ultrasonic exposure. Although increasing the ultrasonic exposure itself is a direct approach to increasing the rate of diffusion, for many imaging applications it is desirable or even necessary to operate at very low ultrasound exposure levels. For example, where an ultrasonographic image is being produced by exposing a living subject to ultrasound, it is desirable to maintain the lowest feasible level of ultrasonic exposure and guidelines have been established for maximum human exposures. Increasing the rate of spontaneous diffusion between the ultrasonographic element and the transport liquid in the absence of ultrasound can have the effect of permitting higher rates of equilibration to be obtained by ultrasonic exposure, but this approach is limited by disadvantages--e.g., background density levels can become objectionably large, loss of image discrimination can result and inconveniently short periods of contact between the ultrasonographic element and the transport liquid can be required.